Although biochar technology is considered a more recent strategy for carbon sequence, the practice of adding charred bio mass a forestry waste to improve soil quality is not new. This process is modeled after a 2,000-year-old practice in the Amazonian basin, where indigenous people created areas of rich, fertile soil which is terra preta (meaning“dark earth”).
Whether these soils were intentionally made or are simply a by-product and waste of farming and cooking practices is still unclear. The fertility of terra preta is significantly higher than the otherwise famously infertile soils of the Amazon forest. This explains why plants grown in terra preta(dark earth) soil grow faster, and are more nutrient-dense, than plants grown in neighboring soils. In fact, terra preta soils continue to hold carbon production still today.
Biochar is produced during pyrolysis, a thermal decomposition of biomass(forestry waste) in an oxygen-limited environment.
The quality of feedstocks, or materials burned, have a direct impact on the quality of the final biochar production. Ideally, clean feedstocks with 10 to 20 percent moisture and high lignin content must be used. Some good examples are field residues and woody biomass(woodin forestry). Using contaminated feedstocks, including feedstocks from railway embankments or contaminated land, can introduce toxins into the soil, drastically increase soil pH and inhibit plants from absorbing minerals. The most common contaminants are heavy metal including cadmium, chromium, copper, lead, zinc, mercury, nickel and arsenic and Polycyclic Aromatic Hydrocarbons.
Biochar can be manufactured through low-cost, small-scale production using modified stoves or kilns, or through large-scale, production, cost-intensive which utilizes larger pyrolysis plants and higher amounts of feedstocks. One of the most common ways to make biochar for on-farm use is through pyrolysis using a top-lit updraft biochar machine to produce charcoal.